2026 Oracle 1z0-830: Java SE 21 Developer Professional Newest Mock Exam

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Oracle 1z0-830 Exam Syllabus Topics:

SectionObjectives
Topic 1: Core APIs- Java standard library usage
  • 1. Collections Framework
    • 2. Date and Time API
      • 3. Streams and functional programming
        Topic 2: Concurrency and Multithreading- Thread management
        • 1. Virtual threads and structured concurrency concepts
          • 2. Thread lifecycle and synchronization
            Topic 3: Database Connectivity (JDBC)- Database interaction
            • 1. SQL execution and result handling
              • 2. JDBC API usage
                Topic 4: Input/Output and File Handling- NIO and file operations
                • 1. Serialization basics
                  • 2. File, Path, and Streams APIs
                    Topic 5: Java Language Fundamentals- Java syntax and language structure
                    • 1. Control flow statements
                      • 2. Data types, variables, and operators
                        Topic 6: Object-Oriented Programming- Core OOP principles
                        • 1. Encapsulation, inheritance, polymorphism
                          • 2. Abstract classes and interfaces
                            Topic 7: Advanced Java Features (Java SE 21)- Modern language features
                            • 1. Virtual threads (Project Loom)
                              • 2. Sealed classes
                                • 3. Pattern matching for switch
                                  • 4. Records and record patterns
                                    Topic 8: Exception Handling and Debugging- Error handling mechanisms
                                    • 1. Try-with-resources
                                      • 2. Checked vs unchecked exceptions

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                                        Oracle Java SE 21 Developer Professional Sample Questions (Q71-Q76):

                                        NEW QUESTION # 71
                                        Given:
                                        java
                                        public class ExceptionPropagation {
                                        public static void main(String[] args) {
                                        try {
                                        thrower();
                                        System.out.print("Dom Perignon, ");
                                        } catch (Exception e) {
                                        System.out.print("Chablis, ");
                                        } finally {
                                        System.out.print("Saint-Emilion");
                                        }
                                        }
                                        static int thrower() {
                                        try {
                                        int i = 0;
                                        return i / i;
                                        } catch (NumberFormatException e) {
                                        System.out.print("Rose");
                                        return -1;
                                        } finally {
                                        System.out.print("Beaujolais Nouveau, ");
                                        }
                                        }
                                        }
                                        What is printed?

                                        Answer: D

                                        Explanation:
                                        * Analyzing the thrower() Method Execution
                                        java
                                        int i = 0;
                                        return i / i;
                                        * i / i evaluates to 0 / 0, whichthrows ArithmeticException (/ by zero).
                                        * Since catch (NumberFormatException e) doesnot matchArithmeticException, it is skipped.
                                        * The finally block always executes, printing:
                                        nginx
                                        Beaujolais Nouveau,
                                        * The exceptionpropagates backto main().
                                        * Handling the Exception in main()
                                        java
                                        try {
                                        thrower();
                                        System.out.print("Dom Perignon, ");
                                        } catch (Exception e) {
                                        System.out.print("Chablis, ");
                                        } finally {
                                        System.out.print("Saint-Emilion");
                                        }
                                        * Since thrower() throws ArithmeticException, it is caught by catch (Exception e).
                                        * "Chablis, "is printed.
                                        * Thefinally block always executes, printing "Saint-Emilion".
                                        * Final Output
                                        nginx
                                        Beaujolais Nouveau, Chablis, Saint-Emilion
                                        Thus, the correct answer is:Beaujolais Nouveau, Chablis, Saint-Emilion
                                        References:
                                        * Java SE 21 - Exception Handling
                                        * Java SE 21 - finally Block Execution


                                        NEW QUESTION # 72
                                        Given:
                                        java
                                        package vehicule.parent;
                                        public class Car {
                                        protected String brand = "Peugeot";
                                        }
                                        and
                                        java
                                        package vehicule.child;
                                        import vehicule.parent.Car;
                                        public class MiniVan extends Car {
                                        public static void main(String[] args) {
                                        Car car = new Car();
                                        car.brand = "Peugeot 807";
                                        System.out.println(car.brand);
                                        }
                                        }
                                        What is printed?

                                        Answer: B

                                        Explanation:
                                        In Java,protected memberscan only be accessedwithin the same packageor bysubclasses, but there is a key restriction:
                                        * A protected member of a superclass is only accessible through inheritance in a subclass but not through an instance of the superclass that is declared outside the package.
                                        Why does compilation fail?
                                        In the MiniVan class, the following line causes acompilation error:
                                        java
                                        Car car = new Car();
                                        car.brand = "Peugeot 807";
                                        * The brand field isprotectedin Car, which means it isnot accessible via an instance of Car outside the vehicule.parent package.
                                        * Even though MiniVan extends Car, itcannotaccess brand using a Car instance (car.brand) because car is declared as an instance of Car, not MiniVan.
                                        * The correct way to access brand inside MiniVan is through inheritance (this.brand or super.brand).
                                        Corrected Code
                                        If we change the MiniVan class like this, it will compile and run successfully:
                                        java
                                        package vehicule.child;
                                        import vehicule.parent.Car;
                                        public class MiniVan extends Car {
                                        public static void main(String[] args) {
                                        MiniVan minivan = new MiniVan(); // Access via inheritance
                                        minivan.brand = "Peugeot 807";
                                        System.out.println(minivan.brand);
                                        }
                                        }
                                        This would output:
                                        nginx
                                        Peugeot 807
                                        Key Rule from Oracle Java Documentation
                                        * Protected membersof a class are accessible withinthe same packageand tosubclasses, butonly through inheritance, not through a superclass instance declared outside the package.
                                        References:
                                        * Java SE 21 & JDK 21 - Controlling Access to Members of a Class
                                        * Java SE 21 & JDK 21 - Inheritance Rules


                                        NEW QUESTION # 73
                                        Given:
                                        java
                                        final Stream<String> strings =
                                        Files.readAllLines(Paths.get("orders.csv"));
                                        strings.skip(1)
                                        .limit(2)
                                        .forEach(System.out::println);
                                        And that the orders.csv file contains:
                                        mathematica
                                        OrderID,Customer,Product,Quantity,Price
                                        1,Kylian Mbappe,Keyboard,2,25.50
                                        2,Teddy Riner,Mouse,1,15.99
                                        3,Sebastien Loeb,Monitor,1,199.99
                                        4,Antoine Griezmann,Headset,3,45.00
                                        What is printed?

                                        Answer: A,C

                                        Explanation:
                                        1. Why Does Compilation Fail?
                                        * The error is in this line:
                                        java
                                        final Stream<String> strings = Files.readAllLines(Paths.get("orders.csv"));
                                        * Files.readAllLines(Paths.get("orders.csv")) returns a List<String>,not a Stream<String>.
                                        * A List<String> cannot be assigned to a Stream<String>.
                                        2. Correcting the Code
                                        * The correct way to create a stream from the file:
                                        java
                                        Stream<String> strings = Files.lines(Paths.get("orders.csv"));
                                        * This correctly creates a Stream<String> from the file.
                                        3. Expected Output After Fixing
                                        java
                                        Files.lines(Paths.get("orders.csv"))
                                        skip(1) // Skips the header row
                                        limit(2) // Limits to first two data rows
                                        forEach(System.out::println);
                                        * Output:
                                        arduino
                                        1,Kylian Mbappe,Keyboard,2,25.50
                                        2,Teddy Riner,Mouse,1,15.99
                                        Thus, the correct answer is:Compilation fails.
                                        References:
                                        * Java SE 21 - Files.readAllLines
                                        * Java SE 21 - Files.lines


                                        NEW QUESTION # 74
                                        Given:
                                        java
                                        void verifyNotNull(Object input) {
                                        boolean enabled = false;
                                        assert enabled = true;
                                        assert enabled;
                                        System.out.println(input.toString());
                                        assert input != null;
                                        }
                                        When does the given method throw a NullPointerException?

                                        Answer: B

                                        Explanation:
                                        In the verifyNotNull method, the following operations are performed:
                                        * Assertion to Enable Assertions:
                                        java
                                        boolean enabled = false;
                                        assert enabled = true;
                                        assert enabled;
                                        * The variable enabled is initially set to false.
                                        * The first assertion assert enabled = true; assigns true to enabled if assertions are enabled. If assertions are disabled, this assignment does not occur.
                                        * The second assertion assert enabled; checks if enabled is true. If assertions are enabled and the previous assignment occurred, this assertion passes. If assertions are disabled, this assertion is ignored.
                                        * Dereferencing the input Object:
                                        java
                                        System.out.println(input.toString());
                                        * This line attempts to call the toString() method on the input object. If input is null, this will throw a NullPointerException.
                                        * Assertion to Check input for null:
                                        java
                                        assert input != null;
                                        * This assertion checks that input is not null. If input is null and assertions are enabled, this assertion will fail, throwing an AssertionError. If assertions are disabled, this assertion is ignored.
                                        Analysis:
                                        * If Assertions Are Enabled:
                                        * The enabled variable is set to true by the first assertion, and the second assertion passes.
                                        * If input is null, calling input.toString() will throw a NullPointerException before the final assertion is reached.
                                        * If input is not null, input.toString() executes without issue, and the final assertion assert input != null; passes.
                                        * If Assertions Are Disabled:
                                        * The enabled variable remains false, but the assertions are ignored, so this has no effect.
                                        * If input is null, calling input.toString() will throw a NullPointerException.
                                        * If input is not null, input.toString() executes without issue.
                                        Conclusion:
                                        A NullPointerException is thrown if input is null, regardless of whether assertions are enabled or disabled.
                                        Therefore, the correct answer is:
                                        C: Only if assertions are disabled and the input argument is null


                                        NEW QUESTION # 75
                                        Which two of the following aren't the correct ways to create a Stream?

                                        Answer: A,F


                                        NEW QUESTION # 76
                                        ......

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